Regulation of an early RNA transcribed from the transforming segment of the adenovirus 2 genome

Abstract

Early cytoplasmic RNA transcribed from the left end of the adenovirus 2 genome (region 1) is composed of two major size classes which migrate as 22 and 13 S RNAs. Previous studies demonstrated that translational inhibitors (such as cycloheximide) stimulate a 10-fold accumulation of early viral RNAs labeled 3–5 hr after infection. One notable exception to the cycloheximide effect is the 22 S RNA transcribed from region 1. To clarify this differential effect of cycloheximide, the metabolism of region 1 RNA was compared in several experiments. The kinetics of accumulation of these RNAs in the absence of drug was analyzed beginning 3 hr after infection. The 13 S size class accumulated more rapidly than the 22 S RNA; after 2 hr of labeling, there was a 3-fold excess of 13 S RNA as compared with cultures labeled for 3 hr. Chase experiments using either actinomycin D in the absence of cycloheximide or cold uridine when cycloheximide was present demonstrated that the 22 S RNA was more stable than the 13 S size class. Thus, a 22 S species is unlikely to serve as precursor to a major smaller RNA. Early RNAs synthesized in the presence of the amino acid analogues canavanine or β-hydroxynorvaline also contained increased amounts of region 1 13 S RNA but not the 22 S size class. To determine the effect of delayed cycloheximide addition, infections were performed in the absence of inhibitors and cycloheximide was then added 4 hr later. Under these conditions, the 22 S RNA synthesized from 4.5–6.5 hr accumulated in increased amounts, comparable to the other early RNAs. The results suggest that a protein synthesized early in infection regulates the cytoplasmic concentration of 22 S RNA.